This invention relates to an apparatus and method of testing a biological fluid.
It is known to test milk produced by dairy cows and other mammals to determine whether the animal is suffering from mastitis. For example, laboratory testing of milk samples taken by milk collection operatives is regularly carried out.
Known such tests involve either determining the number of bacteria cells in the sample for a direct indication of the presence of mastitis, or determining the number of somatic cells, e.g. tissue, blood or other cells, in the sample to provide an indirect indication of the presence of mastitis in the animal. This latter test relies on the fact that in an animal with an infection such as mastitis white blood cells (leukocytes) produced by the animal""s immune system will be transferred into the animal""s milk to combat the pathogens. So a high level of somatic cells in the sample will indicate that an infection is present in the animal.
A problem with known laboratory based testing is that there is inevitably a delay between when the sample is taken and when the test results are available. Mastitis can progress rapidly and so the test results may not be accurately indicative of the state of the disease when for example the animal is next milked. Also a laboratory based test on a sample taken by a collection operative (tanker driver), is most likely to include milk produced by a plurality of animals. Thus such tests, whilst being of some use in determining milk quality from a particular farm, are not useful in advising a dairyman for example, as to which of his animals is suffering from mastitis.
Thus a dairyman needs to be able to perform tests on individual animals which will give a rapid result, so that the dairyman can be alerted to an animal which is suffering from mastitis. In response, the dairyman may decide to dispose of an individual animal""s milk so as not to lower the quality of milk from the herd, and may make a decision either to treat the animal e.g. with antibiotics, or to allow the animal""s own immune system to combat the infection.
In each case, early diagnosis of mastitis is important to enable the dairyman proactively to maintain the quality of the herd""s milk provided for production, and to provide for timely, appropriate treatment of individual animals in the herd.
Milk tests are known which are intended to be performed by a dairyman, which are known as the Californian Mastitis Test (CMT) and the conductivity test. However to perform such tests, the tester needs to make subjective judgements which a dairyman may not be sufficiently skilled to make. Also such tests exhibit a lack of sensitivity for detecting subclinical mastitis, and the CMT lacks accuracy at somatic cell count levels required by current rules and regulations. Such tests do not readily lend themselves to use in the context of a cowshed where cows may be milked.
Portable biological fluid testing kits are known, for example from U.S. Pat. No. 5,827,675 but these are complex to use and do not lend themselves readily for use by say, a dairyman, in the field.
According to one aspect of the invention we provide an apparatus for testing a biological sample from an animal for the presence of disease in the animal, the apparatus including a container, a dipstick and a luminometer, an end of the dipstick being adapted to be inserted into the sample so that a predetermined amount of the sample becomes attached to the dipstick and takes part in a reaction in the container which produces light emissions, the luminometer being adapted to receive the container and to be operated whereby a determination of the level of bacteria and/or somatic cells in the sample and hence of the disease in the animal is made, by sensing light emissions from the container.
The invention has been primarily but not exclusively developed for use in testing raw milk.
Thus utilising an apparatus in accordance with the invention, milk from an individual milk producing animal can be tested by, for example, a dairyman as soon as or soon after the milk is produced, simply, and because the luminometer is capable of measuring light emissions from the container, testing does not rely on subjective determinations.
In order that a luminometer may be used, it is essential that the milk or other fluid attached to the dipstick reacts with an agent on the dipstick and/or the reagent in the container to create a light producing reaction. The amount of light produced preferably is determined by the number of somatic cells in the milk attached to the dipstick whereby the test is an indirect test, i.e. the presence of disease in the animal is indicated by the number of somatic cells in the sample rather than the number of bacterial cells in the sample. However the invention may be applied to direct testing methods which test for bacterial cells in the sample, using a suitable reagent.
Preferably the container contains an extractant and the contents of the somatic cells in the milk or other fluid attached to the dipstick is released on contact with the extractant. The extractant may be contained in a chamber of the container prior to testing and the end of the dipstick may be supported in the container out of contact with the extractant until testing is performed. For example, a chamber may be provided in the container between a closed end of the container and a membrane within the container, and the membrane may be ruptured to enable the milk or other fluid attached to the dipstick, and the extractant, to be brought into contact during testing. The membrane may be of plastic, or a metal or a combination of these such as for example only, metalized Mylar.
The dipstick may be moveable within the container from a position in which the dipstick is supported out of contact with the membrane, and a position in which the end of the dipstick is in contact with the extractant, such movement rupturing the membrane.
In one arrangement the dipstick may be supported by a cap which closes an open end of the container until removed, the cap including a frangible connection which is broken to enable the dipstick to move within the container to rupture the membrane. Thus the dipstick and the container are adapted for single use.
The cap of the container may include indicia means so that the container can be uniquely identified and readily indexed with an animal which produces the milk or other biological fluid sample. In one arrangement, such indicia means may include one or more wings on which information may be provided e.g. by writing.
The container is preferably tubular, but preferably is of a non-circular cross section and is receivable in a corresponding non-circular opening of the luminometer so that the container is constrained to a desired orientation in the opening e.g. to maximise light collection from the container.
The extractant may typically be a lysate, which ruptures the somatic cells in the fluid, on contact. Thus to facilitate the reaction, preferably the dipstick includes a reagent such as an enzyme to react with cellular components in the milk or other biological sample.
The dipstick most conveniently is made of a plastic material. To prevent neutralisation of the enzyme or other reagent carried on the dipstick by the material from which the dipstick is made, preferably a barrier is provided betwveen the agent and the material of the dipstick. In one arrangement, the agent may be carried on an absorbent pad which is adhered or otherwise secured to the dipstick. One such pad is an absorbent fabric pad made of cottonor other natural fibres for examples. Such a pad may be configured to absorb a known amount of milk or other fluid, so that a known amount of fluid is used in the test. The dipstick may be configured to encourage excess fluid not to attach to the dipstick. For example the end of the dipstick may be pointed.
One suitable reagent is firefly luciferin together with the enzyme luciferase.
The luminometer may be configured to count all photons emitted as a result of the luciferin/luciferase reaction or only photons in a particular frequency range. Thus all photons or only photons specific to the luciferin/luciferase chemical reaction may be sensed by the luminometer as desired.
According to a second aspect of the invention we provide a method of testing a biological sample from an animal for the presence of disease in the animal, the method including inserting an end of a dipstick into a sample of the biological fluid whereby a predetermined amount of the sample is attached to the dipstick, inserting the dipstick into a container whereby the predetermined amount of the sample takes part in a reaction in the container which produces light emissions, inserting the container into the luminometer and operating the luminometer to sense light emissions from the container and determining a level of bacteria in the sample and providing an output from the luminometer
The method of the second aspect of the invention may utilise any of the features of the apparatus of the first aspect of the invention.
According to a third aspect of the invention we provide a dipstick assembly for use in an apparatus according to the first aspect of the invention, the assembly including a dipstick having a free end which is adapted to be dipped into a biological fluid sample, and to attach to the dipstick a predetermined amount of the sample for use in a subsequent reaction, characterised in that the sample is milk and the dipstick carries an agent which takes part in the subsequent reaction to provide light emissions.
The dipstick of the assembly may have any of the features of the dipstick of the apparatus of the first aspect of the invention.
According to a fourth aspect of the invention we provide in combination a container containing a test reagent and a biological fluid sample to be tested, and a luminometer device, the reagent and the sample reacting to produce light emissions, the luminometer being adapted to receive the container and to sense the light emissions, and wherein the container and the luminometer are adapted so that the container, when received in the luminometer, is received in a preferred orientation.
The reagent may be contained within the container by virtue of being attached to the dipstick.
For example the container may be elongate and of non-circular cross section, and the luminometer may include an opening of cross section corresponding to the cross section of the container. Thus the container may be orientated to maximise light collection and to ensure test consistency between different samples.
The container and/or the luminometer may have any of the features of the container and/or luminometer of the apparatus of the first aspect of the invention.